The present invention relates to an optical recording device, an optical reproducing device, and an optical memory medium that are arranged so that a control pattern is recorded in the optical memory medium of a magnetic super-resolution type, and that a reproducing power of a light beam is controlled according to a reproducing signal obtained from the control pattern.
Recently, magneto-optical disks of the magnetic super-resolution type from which recording marks smaller than a spot diameter of a light beam can be reproduced have drawn attention. Such a magneto-optical disk is, for instance, provided with a recording layer and with a reproducing layer having in-plane magnetization at room temperature, and reproduction of the same is carried out in the following manner. During reproducing, a light beam is projected onto the reproducing layer side of the magneto-optical disk. Then, part of the area of the reproducing layer within the light beam spot is heated to above a predetermined temperature, and the magnetization of this portion (hereinafter referred to as an aperture) shifts from in-plane magnetization to a perpendicular magnetization conforming to that of the recording layer beneath the aperture. In this way, recorded marks smaller in diameter than the light beam spot can be reproduced.
By the foregoing method, however, changes in the ambient temperature during reproducing tend to cause the optimum reproducing power of the light beam to fluctuate accordingly, even in the case where the driving current for generating the light beam is kept constant.
If reproducing power is much stronger than the optimum level, the aperture formed becomes too large. Consequently, output of reproducing signals from tracks adjacent to the track being reproduced is increased, the proportion of noise signals included in the reproduced data increases, and reading errors are more likely to occur. If reproducing power is much weaker than the optimum level, the aperture becomes smaller than the recorded mark, and the reproducing signal output from the target track is reduced. Accordingly, the proportion of noise signals included in the main signal increases, and reading errors are more likely to occur in this case as well.
A technique to cope with the foregoing problem is disclosed in the Japanese Publication for Laid-Open Patent Application No. 7668/1999 (Tokukaihei 11-7668 [publication date: Jan. 12, 1999]). In that technique, two types of patterns for reproducing power control (hereinafter referred to as reproducing-power-control patterns) of different mark-space lengths are reproduced, and reproducing power is controlled so as to bring close to a predetermined value a ratio of amplitudes of reproducing signals obtained from these recorded marks. By this means, reproducing power is maintained at an optimum value, and the likelihood of reading errors is reduced. Here, in the case where the shorter pattern among the two types of reproducing-power-control patterns has a recording length of 1T (T represents the minimum recording length), the S/N ratio becomes too low since a signal from the pattern has a small amplitude value. On the other hand, in the case where the foregoing pattern has a recording length of 2T, sensitivity to changes in the amplitude ratio cannot be obtained at the level required for detection of an optimum aperture since a signal from the pattern has a great amplitude value. Therefore, the technique disclosed by the foregoing publication utilizes 1T- and 2T-patterns that are present together.
FIG. 5 is a block diagram schematically illustrating an arrangement of such a recording-reproducing device. FIG. 6 is a view schematically illustrating a structure of a magneto-optical disk 20 used in the foregoing recording-reproducing device. FIG. 7 is an explanatory view of short-mark/space patterns and long-mark/space patterns for reproducing power control. The following description will explain the foregoing recording-reproducing device, particularly its reproducing power control operation, with reference to these figures.
As shown in FIG. 6, in a magneto-optical disk 20, data are recorded in each sector 200 as a unit. A short-mark/space recording area 103 is provided in a front part of each sector 200, and a long-mark/space recording area 104 is provided therebehind. Furthermore, a data recording area 105 for recording information data is provided behind the long-mark/space recording area 104.
As shown in FIG. 7(a), a short mark having a mark length of 2T is repeatedly provided at an inter-mark distance (space) of 1T in the short-mark/space recording area 103. As shown in FIG. 7(b), a long mark having a mark length of 8T is repeatedly provided at an inter-mark distance (space) of 8T in the long-mark/space recording area 104.
The following description will explain an operation of recording reproducing-power-control patterns in a magneto-optical disk 20 arranged as described above.
A light emitted from a semiconductor laser 2 is projected onto the short-mark/space recording area 103 disposed in the front part of the sector 200 on the magneto-optical disk 20. Here, a driving current supplied to the semiconductor laser 2 from the laser power control circuit 13 has a high power for recording use.
Besides, simultaneously, an external magnetic field is applied onto the magneto-optical disk 20 from a magnetic head 18. Here, a power control pattern generating circuit 16 switches the polarity of the magnetic head 18 at time intervals of 1T and 2T.
In so doing, the short marks having a mark length of 2T each are recorded at inter-mark distances of 1T each in the short-mark/space area 103 as shown in FIG. 7(a). Likewise, the power control pattern generating circuit 16 switches the polarity of the magnetic head 18 at time intervals of 8T, thereby causing the long marks having a mark length of 8T each to be recorded at inter-mark distances of 8T each in the long-mark/space area 104 as shown in FIG. 7(b).
The following description will explain a reproducing operation of the foregoing recording-reproducing device. Upon projection of light emitted from the semiconductor laser 2 onto the short-mark/space recording area 103 in the sector 200 on the magneto-optical disk 20, light is reflected from the short-mark/space pattern recorded in the area. This reflected light is converted by a photo-diode 3 into a reproducing signal. The reproducing signal is sent to an amplifier 4 where the reproducing signal is amplified to a level in a range suitable for input into an A/D converter 5 after low-frequency components are removed from the reproducing signal. The reproducing signal is subsequently subjected to A/D conversion by the A/D converter 5, and further, it is inputted to the short-mark/space amplitude detecting circuit 9 where an amplitude value of the short-mark/space pattern is determined. Likewise, reflected light from the long-mark/space recording area 104 is processed by means of the photo-diode 3, the amplifier 4, the A/D converter 5, and the long-mark/space amplitude detecting circuit 8, so that an amplitude value of the long-mark/space pattern is determined.
Incidentally, the A/D conversion is carried out at timings by clocks extracted from the respective reproducing signals by a reproducing clock extracting circuit 19. The short-mark/space pattern and long-mark/space pattern thus determined are inputted into a division circuit 11 and an amplitude ratio thereof is outputted therefrom. This detected amplitude ratio and a standard amplitude ratio are compared by a differential amplifier 12. The driving current applied to the semiconductor laser 2 is controlled by a laser power control circuit 13 so that feedback causes the difference as a result of the foregoing comparison to become smaller.
After the laser light driving current is controlled so that an optimum reproducing power is applied, the emitted light is projected onto the data recording area 105, and reflected light therefrom is inputted to the photo-diode 3, the amplifier 4, the A/D converter 5, and the reproducing data processing circuit 10. Consequently, reproduced information data are outputted at a lower error rate. Then, when the reflected light reaches the next sector, the same process is repeated, so that the reproducing power is set to a new optimum level.
As described above, the conventional recording-reproducing device is arranged as follows: the area for recording the marks for reproducing power control is provided in each sector, that is, dispersedly on the whole, so that the quantity of the reproducing signal for reproducing power control is detected at each sector. This enables control of the reproducing power to respond within a short time to rapid fluctuations in the optimum reproducing power.
However, the foregoing conventional recording-reproducing device have problems as described below.
[PROBLEM 1]
A/D conversion in the conventional recording-reproducing device is, as described above, carried out at timings by the clocks extracted from the reproducing signals by the reproducing clock extracting circuit 19. Therefore, in the case where the frequency and phase of the clock thus extracted shift from normal values, an amplitude value detected of the short-mark/space also shifts from a true value. Consequently, the reproducing power of the light beam controlled according to the foregoing detected values become abnormal. This results in, far from reproduction with a low error rate, deletion of recorded data, and what is worse, damage to the semiconductor laser.
[PROBLEM 2]
FIGS. 8(a) through 8(i) are explanatory views illustrating the clock extracted from the reproducing signal of the short-mark/space pattern in the case of the conventional arrangement. When the short-mark/space pattern in which short marks having a mark length of 2T each are formed at inter-mark distances of 1T each as shown in FIG. 8(a) is reproduced, a reproducing wave-form as shown in FIG. 8(b) is obtained. By binarizing the wave-form at the 0 level, a binary signal with edges corresponding to the mark ends as shown in FIG. 8(c) can be obtained. Accordingly, a clock having phases corresponding to the edges as shown in FIG. 8(d) can be extracted. By carrying out the sampling for the A/D conversion at timings by the rise of this clock, the reproducing wave-form can be sampled at optimal phases as shown with ∘ in FIG. 8(e).
In the short-mark/space pattern, however, the marks and the spaces are different in length, and therefore, the resulting reproducing signal contains low-frequency components. The low-frequency components are removed when the reproducing signal passes through the amplifier 4. This removal of low-frequency components is realized by a high-pass filter (HPF) in the amplifier 4, that operates with a certain time lag, though the level of the time lag varies with the time constant (constant representing the responsiveness).
Therefore, upon reproduction of the front part of the short-mark/space recording area 103, as described above, the adequate clock can be extracted. However, as the low-frequency components are lost, the reproducing wave-form shifts so as to become vertically symmetric with respect to the 0 level as shown in FIG. 8(f) Therefore, in the case where the reproducing wave-form is sampled at rising timings of the clock shown in FIG. 8(h) whose edges have phases corresponding to the edges of the binary signal shown in FIG. 8(g). Consequently, as shown in FIG. 8(i), the wave-form is sampled at a phase with a shift of xc2xc clock from the optimal phase.
This results in that a detected amplitude value of the short-mark/space greatly shifts from a true amplitude value, and the reproducing power of the light beam controlled based on the detected amplitude value also has an abnormal level. This results in, far from reproduction with a low error rate, deletion of recorded data, and what is worse, damage to the semiconductor laser.
The object of the present invention is to provide an optical recording device, an optical reproducing device, and an optical memory medium for use with the same that allow an appropriate amplitude value to be determined by reproducing a reproducing power control pattern according to a clock having stable phases.
An optical recording device of the present invention is an optical recording device that records information in an optical memory medium, and to achieve the foregoing object, the device is characterized by including (1) first pattern generating means for generating a signal corresponding to a power control pattern for control of a reproducing power of a light beam, (2) second pattern generating means for generating a signal corresponding to a phase adjusting pattern for adjusting a phase of a reproducing clock to be used upon reproduction of the power control pattern, and (3) pattern recording means for recording the phase adjusting pattern and the power control pattern in the stated order in each sector of the optical memory medium by switching between an output of the first pattern generating means and an output of the second pattern generating means.
According to the foregoing arrangement, the phase adjusting pattern is recorded in each sector. Therefore, a reproducing signal from the short-mark/space pattern recorded behind the phase adjusting pattern is sampled according to the clock whose phases are precisely adjusted, so that an amplitude value of the reproducing signal can be determined. Consequently, the reproducing power control can be stably carried out at any time.
An optical reproducing device of the present invention is an optical reproducing device for reproducing an optical memory medium in which recorded are a power control pattern for controlling a reproducing power of a light beam and a phase adjusting pattern for adjusting a phase of a reproducing clock to be used upon reproduction of the power control pattern, and to achieve the foregoing object, the device is characterized by including (1) phase adjusting means for adjusting the phase of the reproducing clock according to the phase adjusting pattern, (2) A/D converting means for, at the timing of the output of the phase adjusting means, carrying out A/D conversion of a reproducing signal of the power control pattern, (3) amplitude detecting means for, from an output of the A/D converting means, detecting an amplitude value of the reproducing signal of the power control pattern, and (4) power control means for controlling a reproducing power according to the amplitude detected by the amplitude detecting means.
According to the foregoing arrangement, the phases of the reproducing clock are adjusted by means of the recorded phase adjusting pattern. Therefore, a reproducing signal from the short-mark/space pattern is sampled according to the stable phases at any time, so that an amplitude value thereof can be determined. Consequently, the reproducing power control can be stably carried out.
Furthermore, an optical memory medium of the present invention is, to achieve the foregoing object, characterized by having sectors each of which includes (1) a power control pattern recording area for recording a power control pattern for controlling a reproducing power of a light beams, and (2) a phase adjusting pattern recording area for recording a phase adjusting pattern for adjusting a phase of a reproducing clock to be used upon reproduction of the power control pattern, the phase adjusting pattern recording area being provided before the power control pattern recording area.
According to the foregoing arrangement, the phase adjusting pattern is recorded in each sector. Therefore, a reproducing signal from the short-mark/space pattern recorded behind the phase adjusting pattern is sampled according to the clock whose phases are precisely adjusted, so that an amplitude value of the reproducing signal can be determined. Consequently, the reproducing power control can be stably carried out at any time.
According to the foregoing arrangements of the optical recording device, the optical reproducing device, and the optical memory medium of the present invention, the phase adjusting pattern whose mark and space are equal to each other in length and the power control pattern whose mark and space differ in length are recorded in each sector. With this arrangement, it is possible to determine an amplitude value of the power control pattern according to the clock having stable phases during reproducing. Consequently, information data can be reproduced with a precise and optimum reproducing power at any time.
Furthermore, with the synchronous pattern that is different from both the phase adjusting pattern and the power control pattern and that is recorded immediately before the power control pattern, the sampling of the power control pattern can be started in response to detection of the synchronous pattern during reproducing. This enables to surely detect an amplitude value of the power control pattern.
Furthermore, by recording the phase adjusting pattern and the power control pattern in a front part (header) of each sector, stable adjustment of the phases of the reproducing clock and stable reading of an amplitude from the power control pattern can be realized.